EM tracking systems for use with ultrasound and other imaging modalities

ABSTRACT

An EMT system for use in ultrasound and other imaging modality guided medical procedures. The system includes a tool set of various components to which EM sensors can be releasably secured. Thus, the sensors can be reused, notwithstanding the disposal of other components of the tool set. Various components of the tool set include keying elements to facilitate their registration to the anatomy of the patient undergoing the procedure via the EM sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Provisional Application Ser. No.61/100,870, filed on Sep. 29, 2008, entitled EM Tracking Systems For UseWith Ultrasound Transducers, which application is assigned to the sameassignee as this application and whose disclosure is incorporated byreference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

“Not Applicable”

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

“Not Applicable”

FIELD OF THE INVENTION

This invention relates generally to medical instrument tracking systemand more particularly to tools sets enabling the use of electromagnetic(EM) field multidimensional tracking technology for instrument guidancewithin a patient using medical images (both 2-D and 3-D data sets ofreal time and/or delayed and/or fused images) registered to a patient.

BACKGROUND OF THE INVENTION

Ultrasound has received widespread acceptance as a useful diagnostictool by providing an image of the internal area of inquiry by emissionof very high frequency sound waves from a transducer (commonly called a“probe”) placed in contact with the patient's skin adjacent that area ofinquiry. Repeated arrays of ultrasonic beams scan that area and arereflected back to the transducer, where the beams are received and thedata transmitted to a processing unit. A processing unit, to which theprobe is connected, analyzes the information and composes a picture fordisplay on an associated monitor screen. For some applications thedetermination of the precise position or location of the probe in realtime with respect to the patient's body is desirable, e.g., tocorrelate, register or “fuse” the ultrasonic image to other scans(digital image sets), such as CT scans, MR scans, PET scans, and thelike. This real time correlation matched with targeting software can becombined with real time tracking and navigation systems and devices tonavigate an instrument within a patient for minimally invasiveprocedures. In other settings such as CT, when ultrasound is notavailable or useful virtual navigation of an instrument within a patientalso may be image-guided by having the images registered to the patientusing fiducial markers and also registered to a navigation and trackingdevice or system using recently acquired volume images (data sets) thatare then co-registered to both the images and the navigation system.

Optical and electromagnetic tracking (EMT) technologies are twonon-mechanical, real-time, approaches for accurate instrument trackingand navigation using appropriately registered volume images (digitaldata sets). Both optical and electromagnetic technologies haveadvantages and limitations, but on balance the technological advantagesof EMT for minimally invasive procedures are dominant. In particular,EMT is believed to be the preferable technology because of the abilityto track objects inside the body (beyond line-of sight) and the compactsize of the tracked sensors. These powered sensors typically provideposition and orientation data sets of 5 or 6 degrees-of-freedom (DOF)and combined with the electronic cables required are relativelyexpensive.

EMT systems that support image fusion and instrument tracking arecommercially available and disclosed in the patent literature. Theytypically enable determination of 5 or 6 DOF orientation and position ofan instrument, such as a needle, by determining location, orientation,and/or positioning information relative to some coordinate system. Forexample, Ascension Technology Corporation makes 5 and 6 DOF position andorientation tracking devices suitable for various medical applications,e.g., to navigate, localize, and guide medical instruments forimage-guided procedures. Other manufacturers/suppliers of EM trackingsystems include Polhemus, Inc. Northern Digital Inc. and Medtronic, Inc.Suppliers of software, tracked needles and other instruments forclinical use that utilize these technologies in medical proceduresinclude Traxtal Corporation and Veran Medical. Image fusion incombination with ultrasound is available from Traxtal, Inc., GEHealthcare Ultrasound and Esaote Ultrasound, among others.

Typically these tracking systems use the attenuation of orientedelectromagnetic signals to determine the absolute position andorientation of a sensor, relative to a source, e.g., a magnetic fieldgenerator. The source and the sensor are connected via cables to anelectronics module, which contains a microcomputer and associatedelectronics of the system. The source typically includes threeorthogonal coils that are pulsed in rotation, one after another. Eachpulse transmits a radio frequency electromagnetic signal that isdetected by the sensor. The sensor also contains two or three orthogonalcoils, which measure the strength of the signal from the current sourcecoil. By using the known pulse strength at the source and the knownattenuation of the strength with distance, the position and orientationof the sensor coils can be calculated by the system via triangulationtechniques.

Utilizing EM sensors with ultrasonic probes can be accomplished bypermanently mounting the sensor(s) on the probe or by building suchsensor(s) into the probe. However, the permanent mounting approach maynot be desirable if the probe is also intended to be used inapplications wherein its position need not be determined. Also, theinclusion of such sensor(s) permanently on or in the probe will likelyincrease the cost, complexity and service requirement of the probe.Therefore external attachment, when needed, has become the commerciallydominant approach. The challenge in this case is to locate and attach,when required, the removable sensor(s) to the probe in a way that thatis quick, secure and ergonomic. Thus, the use of some releasablemounting system has become a required element for registration andfusion of volume image data sets from CT, MR, PET, etc. for use duringreal time ultrasound imaging. This has been done by several companies todate, including GE Healthcare Ultrasound, Hitachi and Esaote Ultrasound.

In U.S. Letters patent application Ser. No. 12/111,387, filed on Apr.29, 2008, entitled “Bracket for Mounting At Least One Position DetectingSensor On An Ultrasonic Probe”, which is assigned to the same assigneeas this invention and whose disclosure is incorporated by referenceherein, there is disclosed a bracket for use with an ultrasoundtransducer to releasably mount at least one sensor of alocation/tracking system on the transducer and serves as one uniquesolution to fulfill this commercial ideal.

Other medical components or devices making use of EM sensors have beenprovided as part of an EMT system for use with EM tracked ultrasoundtransducers and also may be used in properly registered CT or CT fusedwith PET or MR image sets without ultrasound. These devices includeneedles of all types, fiducial markers with EMT sensors embedded to aidwith patient and image data registration, and other tracked devices.These tracked devices, especially the needles with sensors in the tip,have been shown to have great advantages for simplifying the safe andaccurate placement of these instruments during minimally invasiveprocedures. However, to date most devices and all existing needles usingEM tip sensors have the sensor(s) permanently attached and must bediscarded after a single use or require time and expense to re-processand re-sterilize. In most cases the cost of these disposable devicesmakes the routine use of EM tracking and navigation cost-prohibitive.Thus, until now, expense has been a serious limiting factor to generaladoption of EM technology for image guidance.

The subject invention entails a complete mechanical tool set that willallow re-use of all the expensive sensor components of an EMT system togreatly reduce costs per procedure in the rapidly expanding market forimage fusion and guidance. While re-using the expensive 5 and 6 DOFpowered (active) EM sensors will require a more complex setup andassembly process for each use, the payoff in reduced cost per procedureis believed to be so critical that the small extra time required forsuch set-up will be gladly tolerated.

The complete EMT tool set for providing image guidance in ultrasoundapplications and for other imaging modalities includes not only thesubject matter of this invention (which will be described shortly), butalso dedicated system software. It is anticipated that most of suchregistration, navigation and image fusion software will be developed andsupplied by the original equipment manufacturers of the imaginghardware.

The system of this invention is in the form of an image fusion andnavigation tool set that includes a number of components. Foremost amongthose components is a specially designed needle (trochar) with areusable EM sensor in the tip of the stylet. Other components include, aspecially designed ultrasound bracket to accept one or more reusable EMsensor(s) and a needle guide (e.g., a slotted needle guide enablingmechanical positioning of the linear instrument within the image planeof the ultrasound transducer). In addition, the subject tool setincludes a releasably securable adapter device for mounting a reusableEM sensor on any needle or elongated medical instrument (e.g., biopsyneedles, syringes, ablation needles, (cryoprobes, RF probes, catheterscontaining a stylet, etc.)) to convert that instrument into an EMtrackable instrument (which will be accurate in the absence ofbending/deflection beyond the attachment point of the device), and skinsurface markers for facilitating three dimensional image registrationand image fusion in certain circumstances (e.g., these may not be usefulin cases where ultrasound is used because more accurate registration maybe achieved using internal anatomic landmarks visible on real timeimages). Those markers can be either the passive or active types.Passive type markers are typically sterile adhesive devices that containonly a radio-opaque marker and/or a marker visible on MR imaging. Thepassive markers of this invention also include a keying feature forregistration using an EM sensor (contained within a housing). Activetype skin surface markers are typically non-sterile adhesive deviceswith embedded or attached EM sensors that can with proper softwaresupport provide continuous real-time automatic registration updates forimage fusion and navigation. Traxtal, Inc. and Veran MedicalTechnologies provide skin surface markers with embedded EM sensors,while the present invention proposes skin surface markers withattachable EM sensors. In accordance with one aspect of the presentinvention in order to provide active markers, passive markers aresupplemented with a mounting bracket that is adapted to receive areusable EM sensor. In addition to the foregoing, it is anticipated thatthe EMT tool set will also include custom sterile disposable cover/drapepackages to allow sterility and re-use without reprocessing of theexpensive EM sensors and connecting cables.

The EMT tool set of the subject invention is intended to support any EMtechnology and function with all imaging modalities alone or incombination (fusion). In particular, the components of the subjectinvention will enable CT, PET-CT, or MR image fusion with or without areal-time ultrasound image and 5 or 6 DOF navigation within the EMfield. Properly applied, the technology of this invention will allowbetter visualization of target lesions in the body and highly accurateinstrument navigation to reach them more quickly and safely. Inparticular, it is anticipated that the subject invention will be used bythe full spectrum of clinicians that employ image guidance for reachinginternal targets within a patient.

The subject invention's image fusion and navigation tool set is designedwith a universal approach allowing components to be used across all OEMimaging platforms. It is anticipated that the subject invention will beutilized by physicians in the following specialties: interventionalradiology, radiology, surgery and cardiology. Anticipated clinicalapplications are biopsy procedures, ablation procedures, catheterplacements, intravascular procedures and endoscopic procedures.

All references cited and/or identified herein are specificallyincorporated by reference herein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention there is provided aninstrument, e.g., a trochar, for insertion into the body of a patientvia a sheath for use in an ultrasound-guided procedure on the patient,with the position of the instrument to be tracked with respect to thebeing by an EMT system. The instrument comprises an EM sensor and afirst member. The first member comprises a first handle and an elongatedlinear stylet secured to and projecting from the first handle. Thelinear stylet has a distal tip portion and a hollow interior cavityterminating adjacent the distal tip portion. The EM sensor has anelectrical cable connected to it. The EM sensor is disposed within thecavity located adjacent the distal tip portion of the stylet and withthe electrical cable extending along the length of and out of thecavity. The sensor and the associated cable are arranged to be removedfrom the cavity of the stylet for reuse.

In accordance with another aspect of this invention there is provided adevice for releasable mounting on an elongated, linear medicalinstrument used in an ultrasound-guided procedure on a patient, with theprocedure being carried out by an ultrasound transducer to enable theposition of the instrument to be tracked with respect to a patient by anEMT system. The instrument has a distal end portion. The devicebasically comprises an EM sensor and a housing for the sensor. Thehousing mounts the sensor and is releasably securable to the instrumentat various positions along the length of the instrument. The housingcomprises a first keying member arranged to be releasably coupled to theultrasound transducer, e.g., to a slotted needle guide mounted on abracket that is mounted on the ultrasound transducer, to enable the EMTsystem to register the sensor with respect to the ultrasound transducer.A second keying member may be provided on the ultrasound transducer,e.g., on the needle guide, so that the distal end portion of theinstrument can be releasably coupled to the second keying member toenable the EMT system to register the distal end portion of theinstrument with respect to the sensor.

In accordance with another aspect of this invention there is provided aninstrument guide and/or a bracket for use on an ultrasound transducer inan ultrasound-guided procedure on a patient by an elongated linearinstrument. The instrument has a distal end portion. The instrumentguide and/or a bracket forms a portion an EMT system and is arranged toreceive the instrument. The EMT system comprises a sensor including ahousing having a first keying member. The instrument guide and/or abracket includes a first keying member adapted to be releasably coupledto the first keying member of the sensor to enable the EMT system toregister the sensor with respect to the ultrasound transducer. A secondkeying member may be provided on the instrument guide and/or a bracketso that the distal end portion of the instrument can be releasablycoupled to the second keying member to enable the EMT system to registerthe distal end portion of the instrument with respect to the sensor.

In accordance with another aspect of this invention there is provided anEMT system for use in an ultrasound-guided procedure on a patient by anelongated linear instrument comprising a first component adapted formounting on an ultrasound transducer and a second component including anEM sensor. The instrument has a distal end portion. The first componentis arranged to receive the instrument. The second component comprises asensor, including a housing for the sensor. The housing comprises afirst keying member. The first component comprises a first keying memberadapted to cooperate with the first keying member of the housing of thesecond component to enable the EMT system to register the sensor withrespect to the ultrasound transducer. The first component mayadditionally comprises a second keying member so that the distal endportion of the instrument can be releasably coupled to the second keyingmember to enable the EMT system to register the distal end portion ofthe instrument with respect to the sensor.

In accordance with another aspect of this invention there is provided anEMT system for use in an ultrasound-guided procedure on a patientcomprising a first component and a second component. The first componentis a marker adapted for securement to the patient. The second componentcomprises a sensor including a housing for the sensor. The housingcomprises a first keying member. The marker comprises a first keyingmember adapted to cooperate with the first keying member of the housingof the second component to enable the registration of the marker withrespect to the body of a patient.

DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation view of an EM trackable trochar constructedin accordance with one aspect of this invention and forming a portion ofthe EMT system of this invention;

FIG. 2 is an enlarged side elevational view, partially in section,showing the distal end of the trochar shown in FIG. 1;

FIG. 3 is an enlarged isometric view of one component assembly of thetrochar of FIG. 1, namely, an assembly of a luer connector and anassociated tubular sheath;

FIG. 4 is an is an enlarged isometric view of another component assemblyof the trochar of FIG. 1, namely, an assembly of a handle and stylet;

FIG. 4A is an enlarged isometric view of the handle shown in FIG. 4;

FIG. 4B is another enlarged isometric view of the handle shown in FIG.4.

FIG. 5 is an is an enlarged isometric view of another component assemblyof the trochar of FIG. 1, namely, an assembly of another or secondhandle, an EM sensor and its associated cable;

FIG. 5A is an enlarged isometric view of one of two sections of thehandle shown in FIG. 5, with the other section of that handle removed;

FIG. 5B is another enlarged isometric view of the section of the handleshown in FIG. 5A;

FIG. 6 is an isometric view of a conventional ultrasound transducer onwhich an EM sensor-mounted bracket is disposed, with a slotted needleguide mounted on the bracket and with an instrument adapter shown beingregistered to the needle guide, all of which form respective portions ofthe EMT system of this invention;

FIG. 7 is an exploded isometric view of the EMT system components shownin FIG. 6;

FIG. 8 is an enlarged isometric view of the instrument adapter shown inFIGS. 6 and 7 having an EM sensor mounted thereon, whereupon thesensor-equipped adapter can be used with any conventional medical needleor other elongated linear medical instrument (not shown) to convert theneedle/instrument into an EM trackable needle/instrument;

FIG. 9 is an exploded isometric view of the sensor-equipped adapter ofFIG. 8;

FIG. 10 is an enlarged top plan view of the sensor-equipped adapter ofFIG. 8;

FIG. 11 is an enlarged side elevation view of one side of thesensor-equipped adapter of FIG. 8;

FIG. 12 is an isometric view of a passive EM marker constructed inaccordance with this invention and having a keying feature constructedin accordance with another aspect this invention to enable asensor-equipped adapter, like shown in FIG. 8, or some othersensor-equipped component to be used to register the marker in the EMTsystem of this invention;

FIG. 13 is an enlarged isometric view showing the sensor-equippedadapter of FIG. 8 mounted on a conventional disposable needle to convertthat needle into an EM trackable needle; and

FIG. 14 is an enlarged isometric view showing the needle of FIG. 13 withthe sensor-equipped adapter mounted thereon in the process of beingregistered to the ultrasonic transducer by the EMT system of thisinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the various figures of the drawing wherein likereference characters refer to like parts, there is shown in FIGS. 1-5Ban EM trackable trochar 20 forming one portion of an EMT system tool setconstructed in accordance with this invention. The EM tracking tool setalso includes several other components, such as an EM sensor-equippedbracket 100 (shown in FIGS. 6-7), a slotted needle guide 200 (also shownin FIGS. 6-7), an EM sensor-equipped adapter 300 (shown in FIGS. 8-10),and an external skin marker 400 (shown in FIG. 12).

The details of each of the components of the tool set of this inventionwill be described later. Suffice it for now to state that the EMtrackable trochar 20 includes an EM sensor and associated componentswhich can be reused, while the other components of that device aredesigned for single use and then disposal.

The bracket 100 is arranged to be mounted on a conventional ultrasonictransducer 2, with a sterile cover (not shown) interposed therebetweenand includes a mount for an EM sensor to enable the ultrasonictransducer to be registered to the anatomy of the patient undergoing theultrasound procedure by the EMT system of which the sensor is acomponent.

The slotted needle guide 200 is arranged to be releasably mounted on thebracket 100 and includes a slot into which a needle, e.g., aconventional biopsy needle, can be inserted and its position detectedand tracked by the ultrasonic transducer.

The EM sensor-equipped adapter 200 (shown in FIGS. 8-10) is arranged tobe mounted on any conventional needle, such as shown in FIGS. 13 and 14,or any other elongated linear medical instrument to convert thatneedle/instrument into an EM trackable needle/instrument.

The external skin marker 300 is a device that is arranged to bereleasably secured (e.g., by a releasable adhesive) to the skin of thepatient to serve as a reference point for the EM tracking system.

Turning now to FIGS. 1-5B the details of the trackable trochar 20 willnow be described, first by describing its various components and then bydescribing its use and operation. The trackable trochar 20 basicallycomprises three component assemblies, namely, a luer lock-sheathassembly 22 best seen in FIG. 3, a handle-stylet assembly 24 best seenin FIGS. 4, 4A and 4B, and a handle-EM sensor assembly 26 best seen inFIGS. 5, 5A and 5B. The handle-EM sensor assembly 26 is arranged to bereused, while the luer lock-sheath assembly 22 and the stylet-handleassembly 24 are each single-use disposable members. Since the handle-EMsensor assembly 26 is arranged for reuse, it will be provided with asterile, single use cover 4 (shown by the phantom lines in FIGS. 1 and5) during use, as will be described later.

The luer lock-sheath assembly 22 is best seen in FIG. 3 and basicallycomprises a conventional luer lock connector 28 and a conventionalsheath or cannula 30 fixedly secured together. The sheath is an elongatelinear tubular member that has an open distal end 32. The luer lockconnector 28 is a hollow member whose proximal end is open at 34, i.e.,is defined by a circular side wall 36. An annular ring 38 projectsoutward from the connector 28 to enable the user to readily grasp theluer lock-sheath assembly 22 during its use (to be described later). Theluer lock-sheath assembly 22 is a disposable, i.e., single use, memberadapted to be releasably mounted on the handle-stylet assembly 24. Tothat end, the circular sidewall 36 of the luer lock-sheath assembly 22is arranged for disposition within an annular shaped recess in thehandle-stylet assembly 24 to releasably frictionally secure thosecomponents together.

The handle-stylet assembly 24 is best seen in FIG. 4 and basicallycomprises a hub 40, a pivotable handle 42 and a stylet 44. The stylet 44is formed of any conventional material, e.g., stainless steel, andincludes a sharpened or pointed distal tip 46. The stylet is hollowalong most of its length, except for its distal end portion as shown inFIG. 2. The hollow interior of the stylet 44 forms a cavity 48 arrangedfor releasable receipt of an EM sensor and its associated cable forminga portion of the handle-EM sensor assembly 26. The stylet can be of anysize, e.g., 16 gauge or smaller, for co-axial technique percutaneoustracking of its tip.

The hub 40 of the handle-stylet assembly 24 is best seen in FIGS. 4A and4B and basically comprises a hollow member having a central recess 50with an opening 52 at its nadir that is in communication with the cavity48 in the stylet 44. An arcuate wall 54 projects upward from the hub 40.Three reinforcing ribs 56 project outward from the hub. The hub alsoincludes a pair of pins 58 projecting diametrically outward from itperpendicular to the longitudinal axis of the hub. The pins serve topivotably mount the handle 42 onto the hub. The top surface of thehandle 42 is flat and includes a finger 60 having a sloped, e.g., 15degree inclined, cam surface 62 on its underside. The finger 60 issomewhat flexible for reasons to become apparent later. A circular wall64 projects downward from the hub 40. The point at which the stylet isconnected to the hub 40 is in the form of a conically shaped projection66. The circular wall 64 extends about the projection 66 to form anannular recess 68 into which the circular proximal portion of the wall36 of the luer lock connector 28 is disposed to frictionally connect theluer lock-sheath assembly 22 to the handle-stylet assembly 24. When soconnected the projection 66 of the handle-stylet assembly is locatedwithin the hollow interior of the luer lock connector 28 and the stylet44 extends down the hollow interior of the sheath or cannula 30 and outits open end 32 (see FIG. 2).

The handle 42 of the handle-stylet assembly 24 is arranged to beselectively moved between a locked position, such as shown in FIGS. 1and 4, to an unlocked position, and vice versa. When the handle 42 is inthe locked position, as best seen in FIG. 4B, the undersurface 62 of thefinger 60 overhangs the top surface of the upstanding wall 54, therebyreleasably locking the handle in that position. When the handle is inthe unlocked position, such as by rotating it in the clockwisedirection, the finger 60 will be off of the upstanding wall 54, therebyfully exposing the hollow interior of the recess 50 in the hub. Thisaction readies the handle-stylet assembly 24 to be coupled to thehandle-EM sensor assembly 26, as will be described later.

The handle-EM sensor assembly 26 is best seen in FIG. 5 and basicallycomprises a handle 70, an EM sensor 72 of conventional construction andan electrical cable 74 connected to the sensor 72. The handle 70 iscomposed of two hollow sections which are adapted to be secured togethervia a pair of screws 76. In FIGS. 5A and 5B only one handle section 70Ais shown. The other section of the handle 70 is of identicalconstruction to section 70A. As can be seen the handle 70 includes adownwardly projecting portion 78 through which a proximal portion of thesensor's cable 74 extends. The sensor cable 74 is a thin, relativelyflexible member. In order to provide some rigidity or stiffness to thecable to facilitate its insertion and disposition and the sensor'sinsertion and disposition within the cavity 48 in the stylet astiffening coating or tube 80 is provided along the entire length of thecable 74 from the sensor 72 up through the projection 78. Each of thehandle sections making up handle 70 is hollow immediately to the rear ofthe projection 78. A cylindrical shield 81 is located within that hollowinterior and serves to transition the proximal end of the small diametersensor cable 74 into a larger and more robust cable section 82 whichexits the handle 70 via a strain relief grommet 84. The top surface ofthe handle 70 is generally flat (like handle 42) and includes adownwardly canted cam surface 86 disposed immediately adjacent theprojection 78. This surface is arranged to be pressed downward by thecam surface 62 on the undersurface of the finger 60 of the handle 42 ofthe handle-stylet assembly 24. This action causes the cover 2 which isdisposed over the handle 70 to be tightly squeezed in the interfacebetween the hub 40 of the handle-stylet assembly 24 and the projection78 of the handle-sensor assembly 26, thereby isolating the sensor.

The assembly and use of the tracking trochar 20 will now be described.To that end, the handle 42 of the handle-stylet assembly 24 is pivotedin the clockwise direction to unlock it. In particular, the handle 42 ispushed downward to rotate it in the clockwise direction so that theundersurface 62 of the finger 60 flexes slightly and rides over the topsurface of the upstanding wall 54 of the hub 40, thereby freeing thehandle. Continued rotation of the handle in that direction will fullyexpose the hollow interior of the recess 50 in the hub 40. This enablesa portion of the handle-EM sensor assembly 26 to be inserted therein sothat the sensor can be disposed within the cavity in the stylet. Beforedoing that the cover 2 is disposed over the handle 70 of the handle-EMsensor assembly 26. The cover 2 is a flexible somewhat resilient member,shaped like a condom, and includes a small opening at one end thereof.The cover is disposed over the handle 70 with the cable extendingthrough the opening. The opening in the cover is sized so that it fitstightly about the stiffening coating or tube 80 on the sensor cable 74.Once the cover 2 is in place on the handle-EM sensor assembly 26, thatassembly is moved with respect to the handle-stylet assembly 24 so thatthe sensor 74 enters into the recess 50, through opening 52 and downthrough the central channel 48 in the stylet 44 until the sensor islocated adjacent the closed distal end of the stylet, e.g., is in aposition like shown in FIG. 2. Once that has occurred the handle 42 canthen be rotated back in the counterclockwise direction, whereupon thefinger 60 flexes somewhat and the cam surface 62 on the underside of thefinger rides over the top edge of the upstanding wall 54 of the hubuntil it clears the inner surface thereof, whereupon the finger snapsdownward to trap the wall, thereby releasably locking the handle 42 inthe closed position. In this position the cam surface 62 engages acorrespondingly shaped surface 86 on the handle 70 of the handle-EMsensor assembly 26, thereby pressing downward on that handle. Thisaction presses the projection 78 deeper into the recess 50 of the hub ofthe handle-stylet assembly, thereby tightly sandwiching the cover 2therebetween to effectively isolate the sensor from the ambientsurroundings and releasably lock the two assemblies 24 and 26 together.The stylet of the connected assemblies 24 and 26 can now be insertedinto the luer lock-sheath assembly 22. To that end, the distal end ofthe stylet 44 is inserted into the open proximal end 34 of the luer lockconnector and down through the open end 32 of the sheath until theconically shaped projection 66 of the hub of the handle-stylet assembly24 is fully within the hollow interior of the luer lock connector, i.e.,the trackable trochar is in the configuration as shown in FIG. 1. Atthis point it is ready for use.

The EM sensor 72 enables the trackable trochar 20 to be tracked duringits use, e.g., during any ultrasonically directed procedure, in aconventional manner by means of any suitable EM tracking system. Forexample, the trackable trochar 20 can be inserted percutaneously intoany portion of the body of the patient while the EMT system is operatedin conjunction with the ultrasound probe to monitor the trochar'sposition. Once in the desired position, the luer lock-sheath assembly 22can be held in position by the user of the device while thehandle-stylet assembly 24 and the handle-EM sensor assembly 26 arewithdrawn as a unit, leaving the luer lock-sheath assembly 22 in place.Any elongated instrument (not shown) can then be introduced through theluer lock-sheath assembly 22 into the patient's body to accomplish thedesired procedure, e.g., a biopsy procedure, an ablation procedure, acatheter placement, an intravascular procedure, and endoscopicprocedure, etc.

The removed handle-stylet assembly 24 can then be disconnected from thehandle-EM sensor assembly 26 and discarded. That disconnection isaccomplished by pivoting the handle 42 of the handle-stylet assembly 24in the clockwise direction to free the finger 60 from the upstandingwall 54 of the hub, as described above. The handle-EM sensor assembly 26can then be moved with respect to the handle-stylet assembly 24 towithdraw the sensor 72 and its cable 74 from the interior of the stylet44. The cover 2 can then be removed from the handle-EM sensor assembly,whereupon that assembly will be ready for reuse, i.e., introduction intothe hollow interior of a new handle-stylet assembly after a new cover isplaced on it.

As should be appreciated from the foregoing the trackable needle trochar20 is arranged for insertion into the body of a patient via the sheath30 for use in an image guided procedure on the patient, with the tipposition of the instrument to be tracked with respect to the patient byan EMT system. This is critical because of the high likelihood ofbending of the instrument during positioning proximal to the sensor. Ifthis weren't the case then having the sensor attached further up theshaft would be equally accurate and satisfactory in all cases. Thesensor is fixed to a handle at a chosen distance away via areinforced/stiffened section of wires. The wires are of equal or smallerdiameter than the sensor in most cases. This is of considerableimportance as the diameter of the sensor becomes the limiting factor inhow small a needle can be used to track the tip. Cabling is providedfrom the handle to a receiver plug that goes to a remote power supplyand signal processing box (not shown). The strain relief manner at whichcable exits the handle is provided in the interest of longevity. Thehandle-EM sensor assembly 26 is a pre-sterilized component that isintended for single use and includes a hollow needle tipped stylet witha handle and an overlying tubular sheath. Preferably, a sterile sleevecover including a small hole in the center of the otherwise closed endwill be included with this disposable stylet and sheath in a kit for theEM sensor portion. The overlying tubular sheath has a distal end and aproximal end at which a connector (e.g., a luer lock) is located. Thedistal end of the tubular sheath is open. The first member comprises afirst handle and an elongated linear stylet secured to and projectingfrom the first handle. The linear stylet has a distal tip portion thatis closed/sealed and a hollow interior cavity terminating adjacent thedistal tip portion. In use, the EM sensor is disposed within the styletcavity and located adjacent the distal tip portion of the stylet withthe stiffened section of electrical cable extending along the length ofand out of the stylet cavity into the second handle through which thesensor wires pass. The handle of the stylet and the handle of the sensorare adapted to be releasably locked together to form a T handle whencombined and to provide a lateral exit for the sensor cable from thehandle of the trochar. The sterile sleeve cover is designed with a smallhole in the tip that is required to let the sensor and the stiffenedsection of wiring leading up to the handle to pass through the sleeveyet allow the sleeve to entirely cover the remaining portion of thereusable handle and cable. The locking section of the stylet handle isdesigned to compress the junction of the stylet handle and the sensorhandle to create a watertight seal using the sterile plastic sleevecover as the sealing gasket at the junction. The tubular sheath 30 is ofa designed length such that when locked in position over the stylet thedistal tip portion of the stylet extends out of the open end of thetubular sheath. Since the sensor, the stiffened section of sensor wire,the sensor handle and the associated cable are fully covered by thecombination of the sealed tip stylet and the sterile sleeve during anyprocedure, and are removed from the cavity of the stylet and uncoveredin a controlled manner only when the procedure is completed, it ispossible to reuse the sensor repeatedly in sterile procedures withoutany need for cleaning or sterilization. The other components of theneedle trochar assembly 20 are all single-use and disposed of at the endof a procedure.

Referring now to FIG. 6 the details of the transducer bracket 100 andits associated components will now be described. To that end, as can beseen the bracket 100 is shown releasably mounted on a conventionalultrasonic transducer or probe 4. As is conventional a sterile cover(not shown) is interposed between the bracket and the transducer. Thebracket 100 serves to releasably mount an EM sensor assembly 6 thereon.The sensor assembly 6 is a reusable component that comprises aconventional EM sensor disposed within a sealed housing 8. With thesensor assembly 6 disposed on the transducer 4, the transducer can betracked with respect to some frame (not shown) or image set to fuse orregister the live ultrasound image to a previously taken image, e.g., aCT scan. This enables the practitioner to navigate the patient'sinternal anatomy to a desired location with assurance. The sealedhousing 8 is a small plastic member having an engineered shape thatsuits various purposes. The primary purpose is for releasably locking tovarious tools in the tool set. Another purpose is a keying feature (tobe described later) for use in registration of the tools for checkingfor accuracy of position within the navigation field or for additionalregistration to images using the passive markers for example. Thesensors placed within this housing may be larger and or less costly thanthe smaller sensors used for the needle trochar 20 with tip trackingdescribed above. These are typically 6 DOF sensors and are preciselylocated within the housing. In addition, to assure accuracy, theirposition relative to the external surfaces/features of the housing iscalibrated and adjusted electronically during production to a chosen,known and reproducible position. This enables the sensors to become amodular component from the standpoint of the software and other tools inthe tool set so that they may be used with most of the tools in the toolset interchangeably.

The bracket 100 basically comprises a ring-like body member 102 which isarranged to snap-fit about a portion of the periphery of the probe 4,e.g., about the lower or distal portion of the probe as shown in FIG. 6.The bracket is preferably an integral member, e.g., a molded componentformed of any suitable material, e.g., plastic. The ring-like bodymember 102 includes an upstanding portion 104 which forms a socket forreleasably mounting the EM sensor assembly 6. The socket 104 is definedby a pair of spaced apart walls 106 which project outward and away fromthe ring-like body portion to form a cavity 108 for receipt of thesensor assembly 6. The upper end of each wall 106 is in the form of aprojecting arm 110. A cylindrical pin 112 extends through the cavity 108between the lower end portions of the walls 106. The pin serves as apivot point about which the sensor assembly can rotate to releasablymount it to the bracket (as will be described shortly). Before doingthat a brief discussion of the details of the construction of the EMsensor assembly 6 is in order. To that end, as best seen in FIG. 9, thesensor assembly 6 basically comprises a generally parallelepiped shapedhousing 8 in which the EM sensor itself (the electrical component, e.g.,the EM coils) is mounted. The cable 10 for the sensor exits the housing8 at the proximal end thereof at a strain relief component. The strainrelief component is of significant importance to longevity of the sensorwhen re-used in this tool set and application(s). The corner of thehousing at the distal end (i.e., the end opposite from the cable egressend) includes a semi-circular shaped recess 12 extending across thewidth of the housing. The radius of the recess 12 is the same or justslightly larger than the radius of the pin 112.

The releasable mounting of the sensor assembly 6 to the bracket isaccomplished by orienting it so that its body 8 is generallyperpendicular to the upstanding body portion 104 of the bracket, withits semicircular recess 12 pointed towards and aligned with the pin 112extending through the bracket's socket. The sensor assembly can then bemounted on the pin (i.e., the pin 112 received within the recess 12) andonce that has been accomplished, the sensor housing can be rotatedupward about the pin, whereupon the proximal end portion of the sensorhousing snap-fits between the projecting arms 110. This actionreleasably locks the sensor assembly 6 in the socket of the bracket 100.In order to guide the sensor into this releasably locked position, thesensor housing 8 includes a pair of guide members 14 on opposite sidesthereof. The inner end of each guide member is in the form of a slopedcam surface 16. As will be appreciated by those skilled in the art, whenthe sensor housing is rotated to lock it in place, the sloped surface ofeach guide will engage the undersurface of a respective one of theprojecting arms 106 and ride thereover until the top (distal) surface ofeach guide member is in abutment with the undersurface of its respectiveprojecting arm. When the sensor assembly is in this position it iseffectively snap-fit or locked in the bracket's socket and is thusresistant from accidental disconnection. If and when it is desired toremove the sensor assembly from the bracket, all that is required is torotate its proximal end downward, i.e., in the clockwise direction, sothat it passes between the projecting arms 106. Once the sensor housing8 is free of those arms the sensor assembly 6 can be removed from thepin in the socket.

The bracket 100 also includes a portion for mounting the heretoforeidentified slotted needle guide 200 on it. In particular, the lower endportion of each wall 106 just below the pin 112 is thickened to form anundercut surface 114 (FIG. 7). The end surfaces of the bottom portion ofeach wall 106 are coplanar with a sloping, guide-receiving planarsurface 116. The surface 116 is arranged to have an inner surface (to bedescribed later) of the needle guide 200 juxtaposed to it when theneedle guide is mounted on the bracket 100. The body portion 104 of thebracket also includes a pair of axially aligned semi-circular convexsurfaces 118 immediately below the lower edge of the guide receivingsurface 116. These convex surfaces serve as pivot points about which aportion of the slotted needle guide 200 can be rotated to releasablysnap-fit the needle guide to the bracket. In the furtherance of thesnap-fitting of the needle guide to the bracket the needle guide alsoincludes a pair of projecting arms 202 (to be described later) that arearranged to snap-fit to respective ones of the undercut surfaces 114 ofthe bracket 100.

The details of the construction of the needle guide 200 will now bedescribed with reference to FIGS. 6 and 7. The needle guide ispreferably formed as an integral unit of any suitable material, e.g., aplastic, and basically comprises a generally T-shaped body member 204having a generally planar front surface 206. That surface is the surfacethat is arranged to be juxtaposed to the receiving surface 116 of thebracket 100 when the needle guide is mounted on the bracket. Theheretofore mentioned projecting arms 202 of the needle guide projectoutward from the top portion of the front surface 206 of the T-shapedbody member and are spaced apart by a sufficient distance to accommodatethe thickened lower portion of the two walls 106 of the bracket 100therebetween. Each of the arms 202 terminates in a flanged tip 208having a cam or sloped outer surface and an undercut lower surface. Thebody member 204 also includes a rear surface 210, from which a pair ofwalls 212 extend. The walls 212 form a channel 214 between them which isadapted to receive a needle or some other elongated instrument to serveas an orientation guide to facilitate in-plane instrument manipulationswithin the channel. A pair of squeeze tabs 216 project backward from theupper end of the T-shaped body member adjacent respective ones of thearms 208. The lower end the T-shaped body member at the front surface206 is in the form of a pair of axially aligned concave recesses 218,each of which is arranged to receive a respective one of the axiallyaligned semi-circular convex surfaces 118 of the bracket 100 to mountthe needle guide 200 on the bracket. That action is accomplished bypositioning the needle guide 200 so that it is tilted slightly downward(i.e., rotated slightly in the clockwise direction) from the orientationshown in FIGS. 6 and 7. The needle guide is then brought into positionso that its concave recesses 218 receive respective ones of thesemi-circular convex surfaces 118 of the bracket. When that has beenachieved, the needle guide 200 can be tilted upward, i.e., rotated inthe counterclockwise direction, whereupon the cam surfaces on the tipsof the arms 202 ride over the front surface of the thickened portions ofthe walls 106 of the bracket, until their undercut portions snap-fitinto engagement with respective undercut portions 114 of those walls.This action effectively snap-fits or locks the needle guide 200 onto thetransducer bracket 100 with sufficient strength to be resistant fromaccidental disconnection. In order to guide the needle guide 200 intothis releasably locked position on the bracket 100, the bracket 100includes a pair of guide members 14 on opposite sides thereof. The guidemembers 14 are like those on the housing 8 of the EM sensor assembly 6.To that end, the inner end of each guide member 14 on the bracket 100 isa sloped cam surface 16. Thus, when the needle guide 200 is rotated inthe counterclockwise direction to lock it in place on the bracket 100,the sloped surface of each guide 14 member will engage the undersurfaceof a respective one of the projecting arms 202 and ride thereover untilthe top surface of each guide member is in abutment with theundersurface of its respective projecting arm. When the needle guide 200is in this position it is effectively snap-fit or locked to the bracketand is thus resistant from accidental disconnection.

If and when it is desired to remove the needle guide 200 from thebracket 100, all that is required is for the user to grasp the twosqueeze tabs 216 between his/her fingers and squeeze them together. Thisaction has the effect of slightly flexing the opposed arms 202 apartfrom each other, thereby freeing the tips of those arms from theundercut surfaces 114 of the bracket 100. Once the tips of the arms 202are free of the undercut surfaces 114 of the bracket, the needle guide200 can be tilted downward (i.e., rotated in the clockwise direction)about the pivot axis formed by the engaging surfaces 118 and 218 untilthe arms 202 are free of the bracket.

As will be described in detail later the needle guide 200 also includestwo keying components, 220 and 240, each of which is adapted to becoupled to corresponding keying components of other portions of the EMsystem of this invention.

Referring to FIGS. 8-10 the details of the EM sensor-equipped adapterdevice 300 will now be discussed. As mentioned earlier this component isarranged to be mounted on any conventional, e.g., disposable, needle500, such as shown in FIGS. 13 and 14, or any other elongated linearmedical instrument (e.g., any needle, rigid catheter, needle on asyringe (i.e., forming a guided syringe, rigid scope, etc) used in animage guided procedure on a patient to convert that instrument into anEM trackable instrument. The device 300 can have different ergonomicgeometries depending on the application. In general, the device 300 hasa receiving feature (to be described later) for accommodating an EMsensor. The sensor is itself permanently fixed (disposed) within aspecial housing like that described above. The construction/shape of thedevice 300 allows the sensor in its housing and covered by a sterilesleeve barrier to be releasably secured to the linear instrument.Moreover, the receiving feature of the adapter device keeps the EMsensor and its housing in a fixed orientation to the linear instrumenteven when the sensor and its housing are covered with the sterile sleevebarrier. This allows a software calculation/determination of thelocation and orientation of the linear instrument in an EM field iflength information is supplied once the device is fixed at a chosenpoint along the long axis of the instrument (as will be describedlater). The sleeve barrier allows re-use of the sensor withoutre-processing or sterilization. As will also be described later, thedevice 300 has a distal end portion with an adjustable cavity toaccommodate and to lock to round, linear instruments of varied diameter(22 Gauge to 8 French). The adapter 300 is comprised of a frame thatholds this attachment feature and a receiving feature for the EM sensorin its housing. The entire device/assembly is releasably securable tothe linear instrument at various positions along the length of theinstrument, but most typically will be located toward one end as farfrom the pointed tip as possible. In the exemplary embodiment describedabove it is made of injection molded plastic and is pre-sterilized forsingle use.

As can best be seen in FIGS. 8 and 9 the adapter 300 basically comprisesa housing 302 having a cavity 304 (FIG. 9) shaped to accommodate an EMsensor assembly 6, like that described previously. The cavity 304 isformed between a pair of side walls 306. A pair of fingers 308 projectupward from respective ones of the side walls 306 at the proximal end ofthe housing 302. A pair of squeeze tabs 310 projects downward fromrespective ones of the side walls 306 opposite to respective ones of thefingers 308. A pin 312 extends between the side walls 306 within thecavity 304. The pin 312 is constructed similarly to the pin 112 of thebracket 100 to enable the releasable pivotable mounting of the sensorassembly 6 in the cavity as will be described shortly. The free end ofeach of the fingers 308 includes an inwardly directed flange 314 forminga cam surface.

The distal end of the housing 302 is solid and includes a passageway orhole 316 extending fully through it. The hole is adapted to receive theelongated body of a conventional needle 500 (FIG. 13) or any otherelongated medical device, e.g., catheter, scope, etc. In order tofacilitate the placement of the adapter on the needle or other elongatedinstrument, the entry to the hole 316 is chamfered. A thumbscrew 318 ismounted on the distal end of the housing so that its free end is incommunication with the interior of the hole 316. When a needle or otherelongated instrument is extended through the adapter's hole 316, theadapter can be positioned at any longitudinal position along theneedle/instrument. Once it is in the desired position, it can bereleasably locked in that position by tightening of the thumbscrew 318,which action brings the free end of the thumbscrew into intimateengagement with the portion of the needle/instrument located within thehole.

The adapter 300 is relatively small, e.g., it takes up onlyapproximately 1 cm of needle/instrument length, and can be mounted on orremoved easily from a straight cylindrical instrument of a range ofsizes (22 G to 8 French). The electrical cable of the sensor assembly 6mounted in the housing 302 exits from the side of the housing, i.e., 90degrees from longitudinal axis of the needle/instrument. This featurereduces the tendency for the sensor-equipped adapter to be accidentallydisplaced along the needle/instrument by pulling on the sensor's cable.

The adapter 300 is preferably a disposable, single-use component, butmay be constructed so that it is reusable. The sensor assembly 6,however, being a relatively expensive component is a reusable. Thus,when used it must be isolated from the ambient surroundings. To that enda thin cover (not shown) shaped somewhat like a condom is placed overthe housing 8 of the sensor assembly 6 before mounting it in the adapter300. The covered sensor assembly can then be releasably mounted in thehouse 302 of the adapter 300. In particular, the releasable mounting ofthe EM sensor assembly 6 in the housing 302 of the adapter 300 isaccomplished by orienting the covered body 8 of the sensor assemblyuntil it is generally perpendicular to the longitudinal axis of theadapter's housing 302, with the semicircular recess 12 at the distal endof the housing 8 being pointed towards and aligned with the pin 312extending through the cavity 304. The sensor assembly 6 can then bemounted on the pin (i.e., the pin 112 received within the recess 312with a portion of the cover interposed therebetween) and once that hasbeen accomplished, the covered sensor housing can be tilted downwardabout the pin, e.g., rotated in the clockwise direction, whereupon theproximal end portion of the sensor housing snap-fits over the camsurfaces at the tips of the projecting arms 308 and then into positionbetween those arms. The guide members 14 operate on the distal surfacesof the arms 308 in a similar manner as described above with respect tothe mounting of the sensor assembly to the bracket 100. This actionreleasably locks (snap-fits) the covered sensor assembly in the adapterso that it is resistant from accidental disconnection.

If and when it is desired to remove the sensor assembly 6 from theadapter 300, all that is required is for the user to grasp the twosqueeze tabs 310 between his/her fingers and squeeze them together. Thisaction has the effect of slightly flexing the opposed arms 308 apartfrom each other, thereby freeing the tips of those arms from the sensorhousing 8. Once the tips of the arms are free of the housing, the sensorassembly with its cover can be rotated about the pin 312 until it can befully removed from the cavity of the adapter. The cover can then bedisposed of and the sensor assembly readied for reuse with anotheradapter 300 or some other component of this system.

As should be appreciated by those skilled in the art with an EM sensorassembly mounted in the adapter 300 and the adapter mounted on a needle500 or any other elongated instrument, the needle/instrument iseffectively transformed into a device that can be readily tracked by anyEM tracking system. Moreover, the adapter 300 is arranged to beregistered to the transducer, which itself is registered in the EMtracking system (e.g., via the EM sensor in the bracket 100).

The registration of the adapter 300 to the transducer is accomplished bymeans of a keying element. That element basically comprises a generallytriangular shaped member 320 projecting outward from the distal surfaceof the adapter's housing 302. The keying element 320 is adapted tocooperate with a correspondingly shaped keying element on the needleguide 200 mounted on the transducer 4 via the bracket 100. The keyingelement on the needle guide for achieving that end is the heretoforeidentified element 220. The details of that element will now bedescribed with reference to FIG. 7. In particular, as can be seen thefree edge of each of the walls 212 forming the channel 214 of the needleguide includes a semi-circular flange 222 extending outward in the planeof the free edge. Each flange includes a projection 224 located thereon.Each projection 224 includes a conical surface forming a portion of itsperiphery and an angled side surface forming another portion of theperiphery of the projection. The angled side surfaces of the twoprojections together define a V-shaped notch between them. The V-shapednotch forms the heretofore identified keying element 220. In particular,the triangular projection 320 of the adapter 300 is adapted to beinserted into the V-shaped notch 220 of the needle guide 200. With theadapter being mounted on a needle 500, like shown in FIG. 13, the needlecan be registered to the transducer in the EM system by merely orientingthe adapter so that its keying element 320 is disposed within theV-shaped notch 220 of a needle guide 200 that is itself mounted on atransducer 4 via a bracket, like bracket 100. Thus, the EMT system canbe provided with information as to the position and orientation of theneedle 500.

The conical peripheral portions of the two projections 224 that arelocated on the flanges 222 together form a projecting member that servesas another keying element of this invention. In particular, that otherkeying element can be used to register other components of the EMTsystem, e.g., the adhesive marker 400, as will be described later.

As should be appreciated from the foregoing, the sensor-equipped adapter300 is suitable to convert any conventional off-the-shelf instrumentinto an EM guided instrument with high accuracy as long as theinstrument doesn't bend. If the needle or other instrument is bendable,so that the location of the tip may not be where expected due to theneedle's bending within the body of the patient, the EMT system shouldbe able to register or track the needle's tip. The subject inventionachieves that end by providing a keying element that enables the systemto register the needle's tip with respect to the sensor-equippedadapter. This is particularly important since the adapter 300 can bepositioned at any longitudinal position along the needle. That keyingelement basically comprises a gusset 240 which is located at theinterface of the wall 212 and the rear surface 210 of the needle guide.Accordingly, after the needle 500 having the sensor-equipped adapter 300mounted thereon has been registered to the EM system by placing theadapter's keying element 320 into the corresponding keying element 220of the needle guide 200, as described above, the tip of the needle canbe registered to the EMT system. That is accomplished by removing theneedle 500/adapter 300 combination from the needle guide 200 andorienting the needle/adapter combination like shown in FIG. 14, so thatthe tip of the needle rests on the gusset 240 while the contiguousportion of the needle extends along the interface of the wall 212 andthe surface 210. The EMT system can then determine the distance betweenthe sensor and the tip of the needle using the information as to wherethe sensor of the assembly 6 in the adapter 300 is now located andoriented and the information previously stored in the system when theneedle/adapter was initially registered to the transducer.

It should be pointed out at this juncture that it is expected that theregistering of the location and orientation of the transducer 4 withrespect to the anatomy of the patient in an ultrasound procedure will beaccomplished by use of the sensor assembly 6 mounted in the bracket 100.However, it is contemplated that such registration can also beaccomplished by using a sensor-equipped adapter 300 and coupling thatadapter to a needle guide mounted on the transducer via a bracket 100.

As mentioned above the EMT system of this invention also includes a skinmarker 400. That marker is a conventional device, e.g., a passivemarker, which has been modified to include a keying element 402 toenable it to be registered into an EMT system using several of thecomponents of this invention. To that end, the skin marker 400 comprisesa disk-like body 404 having an adhesive undersurface and a central hub406 including a top surface in which a conically shaped recess iscentrally located. The bottom surface of the conically shaped recess canbe flat or conical. In any case, the recess forms the keying element402.

The sensor-equipped adapter 300 can be used to register the marker 400into the EMT system after the marker has been positioned on thepatient's body and imaged. To that end, the adapter housing 302 includesa complementary shaped and sized conical projection 322 on its side walllocated generally opposite to the thumbscrew 318. Thus, to register thepassive marker 400, all that is required is to take a sensor-equippedadapter 300 over to the passive marker so that the keying projection 322of the marker is located within the keying recess 402. The EMT systemcan then be operated to register the location of the marker. Once thathas been accomplished the sensor-equipped adapter 300 can be removed.

The marker 400 can also be registered into the EMT system by means otherthan an EM sensor equipped adapter 300. For example, the marker can beregistered by the EM sensor mounted on the transducer bracket 100 viathe use of the needle guide 200. In particular, a transducer having asensor-equipped bracket 100 on which a needle guide 200 is mounted, likeshown in FIG. 6, can be used to register the marker. Such action isaccomplished by manipulating the transducer with the bracket/needleguide mounted thereon into an orientation such that the conicalprojection made up of the two flanged projections 224 of the needleguide 200 (i.e., the needle guide's “other keying element”) fits withinkeying recess 402 of the marker. Once so positioned the EMT system canbe used to record the location of the sensor mounted on the bracket tothus register the location of the marker 400.

The marker 400 can also be registered into the EMT system by thetrackable trochar 20. For such applications it is preferable that thebottom of the keying recess 402 should have a central depression toaccept the pointed tip 46 of the stylet 44. That central depression maybe formed by another conical surface. Thus, to register the marker withthe tracking trochar 20, all that is required is to insert the tip ofthe stylet into the recess 402 so that the tip 46 is at the nadir ofthat recess and then operate the EMT system to take a reading of thelocation of the sensor, and hence of the marker.

The EM sensor in its housing can be used interchangeably with the tool300 and also, with the active markers, with an ultrasound transducer. Tothat end, a first keying member on the sensor housing is arranged sothat it may (if the software is not set up to do this automatically) bereleasably coupled to the ultrasound transducer for system checks. Thekeying member on the sensor housing may be used to calibrate or checkthe calibration of the system (if the software supports this),alternatively the receptacle for the key may be located elsewhere e.g.,to a slotted needle guide mounted on a bracket that is mounted on theultrasound transducer, to enable the EMT system to register the sensorwith respect to the ultrasound transducer. A second keying member may beprovided on the ultrasound transducer, e.g., on the needle guide, sothat the distal end portion of the instrument can be releasably coupledto the second keying member to enable the EMT system to register the(length) distal end portion of the instrument with respect to the sensorwhen using the linear instrument device described above. Alternatively,the software may allow the user to enter this length data manually.

As should be appreciated from the foregoing the system of this inventionhas wide applicability in that it enables registration of thesensor-equipped adapter, definition of the virtual needle position andlength for the ultrasound tracking software, and confirmation ofregistration of the trackable trochar.

Without further elaboration the foregoing will so fully illustrate ourinvention that others may, by applying current or future knowledge,adopt the same for use under various conditions of service.

1. An instrument arranged for insertion into the body of a patient foruse in an image-guided procedure on the patient, the position of theinstrument to be tracked with respect to the patient by an EMT system,said instrument comprising an EM sensor, a first member, and areleasable locking assembly, said first member comprising a first handleand an elongated linear stylet secured to and projecting from said firsthandle, said linear stylet having a distal tip portion and a hollowinterior cavity terminating adjacent said distal tip portion, said EMsensor having an electrical cable connected to said sensor to form areplaceable unit, said replaceable unit being slidably releasablylocated within said cavity, whereupon when said sensor is located at apredetermined position in said cavity adjacent said distal tip portionof said stylet with said electrical cable extending along the length ofand out of said cavity said replaceable unit may be locked in placethereat by said releasable locking assembly, said releasable lockingassembly being arranged to be released to enable said replaceable unitto be slidably removed as a unit from said cavity of said stylet for usein another stylet having a distal tip portion and a hollow interiorcavity terminating adjacent the distal tip portion by introducing saidsensor and said electrical cable of said replaceable unit directlywithin the hollow interior cavity of the other stylet, whereupon saidsensor is located at said predetermined position adjacent the distal tipof said other stylet, said locking assembly being operable to lock saidreplaceable unit thereat.
 2. The instrument of claim 1 wherein theinstrument is arranged for insertion into the body of the patient via asheath, the sheath being a linear tubular member having a distal end anda proximal end, the distal end of the tubular sheath being open, thesheath also including a connector at the proximal end of the sheath, andwherein said first member is releasably securable to the connector ofthe sheath.
 3. The instrument of claim 1 additionally comprising asecond member including a second handle, said cable extending throughsaid second handle.
 4. The instrument of claim 3 wherein said firstmember includes a body portion having a recess and wherein said secondhandle includes a projection through which said cable passes.
 5. Theinstrument of claim 4 wherein said projection of said second handle isarranged to be releasably located within said recess of said bodyportion of said first member.
 6. The instrument of claim 5 additionallycomprising a cover in the form of a flexible sheath having an opening,said cover being arranged to be disposed over said second handle, withsaid cable extending through the opening in said cover wherein a portionof said cover is located at the interface of said projection of saidsecond handle and said recess in said body portion of said first member.7. The instrument of claim 6 wherein said first handle is pivotable andincludes a member adapted to apply a force to a portion of said secondhandle when said first handle is pivoted to a closed position withrespect to said second handle to seal said cover about said cable. 8.The instrument of claim 3 additionally comprising a cover in the form ofa flexible sheath having an opening, said cover being arranged to bedisposed over said second handle, with said cable extending through theopening in said cover.
 9. The instrument of claim 8 wherein said secondhandle is movable to seal said cover about said cable.
 10. Theinstrument of claim 1 wherein said replaceable unit comprises a secondhandle.
 11. The instrument of claim 10 wherein said first handle ismovable with respect to said second handle to form said releasablelocking assembly.
 12. The instrument of claim 11 wherein said firsthandle is pivotable with respect to said second handle.